The present invention generally relates to the detection of ionizing radiation, and particularly to the detection of X-rays.
More specifically, the invention relates to a detector for detection of ionizing radiation, to a device for use in planar beam radiography, and to a method for detection of ionizing radiation.
Gaseous detectors, in general, are very attractive at photon energies lower than approximately 10 keV. The main advantages of gaseous detectors are that they are cheap to manufacture compared to solid state detectors, and that they can employ gas multiplication to strongly (on orders of magnitude) amplify the signal amplitudes. However, at energies exceeding 10 keV the gaseous detectors are less attractive as the stopping power of the gas decreases rapidly with increased photon energy. This results in a heavily deteriorated spatial resolution due to extended tracks of so-called long-range electrons, which are created as a result of the X-ray absorption.
An improved spatial resolution is achieved by a gaseous detector for use in planar beam radiography, in which electrons released by interactions between photons and gas atoms can be extracted in a direction essentially perpendicular to the incident radiation. A detector of such a kind is described in our copending international application No. PCT/SE98/01873 entitled A method and a device for planar beam radiography and a radiation detector and filed on Oct. 19, 1998. Another detector is depicted in the U.S. Pat. No. 5,521,956 issued to Charpak.
When designing a detector for photons of lower energies and using X-rays irradiation of an energy range that includes both lower and higher energies, the higher energy photons will only to a lesser degree be absorbed in the detector due to the relatively short length of the detector.
In some situations, however, it is desirable to also detect high-energy photons as these can carry information that is distinct from that of lower energy photons. For instance, in the field of radiology the absorption coefficients for bone and tissue, respectively, vary quite differently with photon energy.
Accordingly, it is an object of the present invention to provide a detector for detection of ionizing radiation, which employs avalanche amplification, and can operate in a wider energy range, particularly also at higher energies, of incoming radiation than prior art detectors.
It is in this respect a particular object of the invention to provide such a detector that provides for an improved spatial resolution and particularly for an improved energy resolution.
A further object of the present invention is to provide a detector for detection of ionizing radiation, which is effective, fast, accurate, reliable, easy to install and use, and of low cost.
Still a further object of the invention is to provide a detector for detection of ionizing radiation, which is sensitive and can thus operate at very low X-ray fluxes.
Yet a further object of the invention is to provide a detector for detection of ionizing radiation, which can be given a length, in the direction of the incoming radiation, for achieving a desired stopping power, which makes it possible to detect a major portion of the incoming radiation.
Still a further object of the invention is to provide a detector for detection of ionizing radiation, in which electrons released by interactions between photons and gas atoms, can be extracted in a direction essentially perpendicular to the incident radiation. Hereby it is possible to obtain a particularly high spatial resolution.
Yet a further object of the invention is to provide a detector for detection of ionizing radiation, which can operate at high X-ray fluxes without performance degradation and has a long lifetime.
Still a further object of the invention is-to provide a detector for detection of any kind of ionizing radiation, including electromagnetic radiation as well as incident particles, including elementary particles.
These objects among others are, according to a first aspect of the invention, attained by a detector as claimed in Claim 1, and, according to a second aspect of the invention, attained by a detector as claimed in Claim 26.
It is a further object of the present invention to provide a device for use in planar beam radiography, e.g. slit or scan radiography, comprising at least one detector according to the first aspect of the invention.
It is in this respect a particular object of the present invention to provide such a device that can be operated such that an object to be imaged only needs to be irradiated with a low dose of X-ray photons, while an image of high quality is obtained.
Still a further object of the invention is to provide a device for use in planar beam radiography, in which a major fraction of the X-ray photons incident on the detector can be detected, for further counting or integration in order to obtain a value for each pixel of the image.
Yet a further object of the invention is to provide a device for use in planar beam radiography, in which image noise caused by radiation scattered in an object to be examined, is strongly reduced.
Still a further object of the invention is to provide a device for use in planar beam radiography, in which image noise caused by the spread of X-ray energy spectrum is reduced.
Yet a further object of the present invention is to provide a device for use in planar beam radiography, which can operate at high X-ray fluxes without performance degradation and has a long lifetime.
These objects among others are, according to a third aspect of the invention, attained by a device as claimed in Claim 18, and, according to a fourth aspect of the invention, attained by a device as claimed in Claim 36.
It is a further object of the present invention to provide a method for detection of ionizing radiation, which employs avalanche amplification and is efficient in a wider energy range, particularly also at higher energies, of incoming radiation than prior art methods.
It is in this respect a particular object of the invention to provide such a method that provides both for an improved spatial resolution and for an improved energy resolution.
A further object of the present invention is to provide a method for detection of ionizing radiation, which is effective, fast, accurate, reliable, easy to perform, and which can be implemented in a simple and cost effective way.
Still a further object of the invention is to provide a method for detection of ionizing radiation, which is sensitive and can thus operate at very low X-ray fluxes.
Yet a further object of the invention is to provide a method for detection of ionizing radiation, which detects a major portion of the incoming radiation.
Still a further object of the invention is to provide a method for detection of ionizing radiation, in which electrons released by interactions between photons and gas atoms, can be extracted in a direction essentially perpendicular to the incident radiation. Hereby it is possible to obtain a particularly high spatial resolution.
Yet a further object of the invention is to provide a method for detection of ionizing radiation, which can be performed using high X-ray fluxes.
Still a further object of the invention is to provide a method for detection of any kind of ionizing radiation, including electromagnetic radiation as well as incident particles, including elementary particles.
These and other objects are, according to a fifth aspect of the present invention, attained by a method as claimed in Claim 22, and, according to a sixth aspect of the invention, attained by a method as claimed in Claim 37.
Further characteristics of the invention and advantages thereof will be evident from the following detailed description of preferred embodiments of the invention, which are shown in the accompanying drawings.